title: Changes in cerebral blood flow during hyperventilation and CO2-breathing measured transcutaneously in humans by a bidirectional, pulsed, ultrasound Doppler blood velocitymeter.
abstract: We have used a bidirectional pulsed ultrasound doppler system which measures the instantaneous mean velocity across the lumen of a blood vessel in order to determine the relationship between alveolar PCO2 (PACO2) and blood flow in the four arteries supplying the brain in humans. Both high and low PACO2-values were explored. Six subjects, 3 males and 3 females (22-40 years) were studied by use of this non-invasive technique. To increase the PACO2 the subjects were breathing 4, 6 and 8% CO2 in air. PACO2 was reduced by voluntary hyperventilation down to a chosen end-expiratory PCO2 value of about 2.2 kPa. We found a linear relationship between arterial blood flow expressed as a percentage of control level and PACO2 in the range from 3.3 to 7.3 kPa. At the very lowest PACO2 values a levelling off of the response, with flow values of 40 to 45%, was observed. The CO2-reactivities in the 6 persons varied between 28.1 and 30.0%/kPa. The time course and the magnitude of the flow response were similar in all four arteries.
mesh_terms: D000328:Adult; D001783:Blood Flow Velocity; D002245:Carbon Dioxide; D002343:Carotid Artery, Internal / Q000502:physiology; D002560:Cerebrovascular Circulation; D004301:Doppler Effect; D005260:Female; D006801:Humans; D006985:Hyperventilation / Q000503:physiopathology*; D008297:Male; D008722:Methods; D012039:Regional Blood Flow; D014465:Ultrasonics / Q000295:instrumentation; D014711:Vertebral Artery / Q000502:physiology
chemical_list: D002245:Carbon Dioxide